Parkinson's disease (PD) is the second most common neurodegenerative disorder in which the main pathology is selective degeneration of midbrain dopaminergic (mDA) neurons in the substantia nigra. Because of this specific cell loss, PD is considered to be a prime target disease for cell-based therapy. Indeed, numerous clinical and preclinical studies demonstrated the proof-of-principle that cell transplantation is a viable therapeutic regimen for PD treatment once an ideal and unlimited cell source can be established (reviewed in (Redmond, 2002; Li et al., 2008a; Lindvall and Kokaia, 2009). In 2006, Shinya Yamanaka and his colleagues published their groundbreaking work showing that pluripotent stem cells, so called induced pluripotent stem cells (iPSCs), can be generated from somatic cells by retroviral transduction of four reprogramming factors (i.e., Oct4, Sox2, Klf4 and c-Myc)(Takahashi and Yamanaka, 2006). Subsequent successful generation of human iPSCs by similar methods (Takahashi et al., 2007; Yu et al., 2007; Park et al., 2008a) offered the possibility to generate disease- or patient-specific stem cells without destruction of embryos. Indeed, these iPSCs offer unprecedented potentials for biomedical research, disease mechanism study, and personalized cell-based therapies. However, current iPSCs suffer from major drawbacks including multiple viral integrations and remaining transgenes at various chromosomal locations, any of which may cause unpredictable genetic dysfunction and/or tumor formation, making these cells unsuitable for clinical applications (Yamanaka, 2009a). With the long-term goal of developing a personalized cell-based therapy of PD using iPSCs, we propose the following three specific aims. First, based on our preliminary results (Kim et al., 2009a), we will establish iPSC lines from healthy and sporadic PD subjects by a novel, DNA-free reprogramming method (i.e., direct delivery of reprogramming proteins). We will extensively evaluate morphological, gene expression, epigenetic, and in vitro and in vivo differentiation properties to establish iPSC lines exhibiting properties similar to human embryonic stem cells (hESCs). We will compare their properties with those of hESC lines and iPSCs generated by conventional retroviral methods. In addtion, we will investigate their chromosomal integrity by state of the art copy number variation analysis. Second, once authentic iPSC lines are established, we will fully characterize and compare their in vitro differentiation properties into neural progenitors and midbrain DA neurons. We will optimize their differentiation into A9 DA neurons and evaluate the molecular, cellular, and electrophysiological characters of DA neurons from these iPS cells. Third, we will initiate to evaluate the potential functional benefits of these iPSC-derived DA neurons in two rodent models of PD; aphakia mice and 6-OHDA lesioned rats, both of which are well established in our laboratory. Biological and behavioral outcomes of these transplantation studies will be systematically investigated. Overall, our proposed experiments will provide invaluable insights and stepping stones, leading to the development of safe, realistic, and ideal cell source for personalized cell-based therapy of PD.